1. Field of the Invention
This invention relates to a plasma display panel, and more particularly to a front plate of a plasma display panel.
2. Description of Prior Art
Normally, the front plate of a plasma display panel (hereinafter referred to as a PDP) is fabricated by known semiconductor process. These plasma display panels are classified as either transparent type or reflective type in terms of its luminance mechanism. The characteristic of the so-called transparent type PDP is that the fluorescence material is formed on the front plate. On the other hand, in a reflective type PDP the fluorescence material is formed on the rear plate. The reflective type PDP is the topic of the recently researches.
Usually, a plasma display panel includes a front plate and a second plate. A front plate of a plasma display is constituted by forming a plurality of display electrodes including transparent electrodes and auxiliary electrodes on the first substrate. The transparent electrode is normally made of indium tin oxide (ITO). The auxiliary electrode is opaque and normally has a tri-layer structure such as Cr/Cu/Cr or Cr/Al/Cr. Moreover, a plurality of address electrodes, which are orthogonal to the plurality of display electrodes, are formed on the second substrate. A plurality of ribs, parallel to the plurality of address electrodes, are formed on the second substrate for defining a discharge space therebetween. A plurality of fluorescence layers are alternately formed between the plurality of ribs. A voltage is applied between the address electrodes and the display electrodes, ultraviolet light will be generated by the discharge of gas in the discharge space, and the fluorescence layer will absorb the ultraviolet light and emit visible light.
Referring to FIG. 1a, the front plate of a plasma display includes a substrate 10, a plurality of transparent electrodes 12 formed on the substrate 10, a plurality of auxiliary electrodes 14, and a dielectric layer 16. Each of the auxiliary electrodes 14 includes a first portion 141 formed on a corresponding transparent electrode and a second portion 142 directly formed on the substrate. Each second portion 142 of the auxiliary electrode is electrically contacted with a bonding pad (not shown) of plasma display. The dielectric layer 16 covers the transparent electrodes and parts of the auxiliary electrodes. A passivation layer (not showed) then covers the whole surface of the displaying area of the substrate.
Please refer to FIGS. 1b and 1c, which are cross-sectional diagrams of FIG. 1a along line Ixe2x80x94Ixe2x80x2 and line IIIxe2x80x94IIIxe2x80x2, respectively. The dielectric layer 16 covers the first portion 141 of the auxiliary electrodes and a part 1421 of the second portion 142 of the auxiliary electrodes. The other part 1422 of the second portion 142 of the auxiliary electrode is not covered by the dielectric layer 16.
Usually, the dielectric layer is formed by a screen-printing process and then is cured after a sintering process. The dielectric layer will shrink during the sintering process. The second portion 142 of the auxiliary electrode is formed between the dielectric layer 16 and the substrate 10. Because the stress between the dielectric layer and the auxiliary electrode is different from the stress between the auxiliary electrode and the substrate, the shrunk dielectric layer may cause the second portions 142 of the auxiliary electrodes to be peeled from the substrate 10. The peeled electrodes may be oxidized during the high temperature sintering process, and several unwanted black regions will form on the front plate. Moreover, when a voltage is applied on the front plate, the auxiliary electrodes may be broken because of a high voltage drop between the peeled electrodes and the substrate 10. Further, a yellow substrate will be formed on the substrate 10 where the side wall of the dielectric layer 16 intersected with the second portion 142 of the auxiliary electrode. Because of the high voltage between the auxiliary electrode 14 and the substrate 10, the yellow substrate may be formed by a reaction between the auxiliary electrodes and the glass substrate 10. It is so-called xe2x80x9cyellow coloring phenomenonxe2x80x9d, and leads to a color distortion at the edge of the display panel while displaying images. In addition, the manufacturing yield becomes lower since the electrode is easily broken because of the high voltage drop between the auxiliary electrode 14 and the substrate 10.
FIG. 2 is a photograph of the front plate of a conventional PDP. In the picture, the auxiliary electrode is peeled from the substrate at the interface near the boundary of the dielectric layer which is indicated by arrow A. The dielectric layer is shrunk. Because the stress between the glass substrate and the dielectric layer is different from the stress between the auxiliary electrode and the dielectric layer, a stress is occurred between the auxiliary electrode and the glass substrate. The auxiliary electrode will be peeled off and a yellow substrate will also be formed. As long as the auxiliary electrode and the substrate are made of a sodium glass, the yellow coloring phenomenon is unavoidable. According to the understanding of the inventor, all kinds of material for forming the dielectric layer will cause the yellow coloring phenomenon.
Accordingly, to overcome the drawbacks of the prior arts, an object of this invention is to provide a front plate of a plasma display panel that can prevent the auxiliary electrode from being peeled from the substrate at the boundary of the dielectric layer.
Another object of this invention is to provide a front plate of a PDP that can increase the manufacturing yield of the PDP by avoiding the occurrence of yellow coloring phenomenon at the boundary of the dielectric layer.
To achieve the above objects, the layout of the front plate is amended. In the present invention, the front plate of a plasma display panel includes a substrate, a transparent electrode formed on the substrate, and an auxiliary electrode having a first portion formed on the transparent electrode and a second portion directly formed on the substrate. The front plate further includes a dielectric layer covered the transparent electrode, the first portion of the auxiliary electrode, and a part of the second portion of the auxiliary electrode, and an isolating layer formed between the substrate and the second portion of the auxiliary electrode, and under a position where the sidewall or boundary of the dielectric layer contacts the upper surface of the second portion of the auxiliary electrode. The isolating layer is formed to reduce the stress between the auxiliary electrode and the substrate, and therefore, the auxiliary electrode will not be peeled from the substrate. The isolating layer also eliminates the occurrence of the yellow substrate on the substrate where the auxiliary electrode contacts with the boundary of the dielectric layer. The yellow coloring phenomenon can be avoided.